Thermal inkjet-printing devices, such as thermal inkjet printers, operate by appropriately ejecting ink from inkjet-printing nozzles to form images on media such as paper. Ink is ejected from a given inkjet-printing nozzle by using a firing circuit for the inkjet-printing nozzle. The firing circuit includes a heater resistor and a switch. When the switch is closed, current flows through the heater resistor, which heats ink and causes it to eject from the corresponding nozzle. Current firing circuit designs are known as “low-side switch” firing circuits, in which a side of the switch is always connected to a ground, and a side of the heater resistor is always connected to a voltage source. However, such designs can be problematic. If a heater resistor of a given nozzle fails, for instance, the resulting voltage leakage can damage other firing circuits.